import java.util.Scanner;

/**
 * Created with IntelliJ IDEA.
 * Description:递归求斐波那契数列的第 N 项
 * User: zjc
 * Date: 2022-05-09
 * Time: 23:32
 */
public class Project {
    public static void main(String[] args) {
        Scanner sc = new Scanner(System.in);
        int n = sc.nextInt();
        int sum = fac(n);
        System.out.println(sum);
    }
    public static int fac(int n){
        if(n==1||n==2){
            return 1;
        }else{
            return fac(n-1)+fac(n-2);
        }
    }
}
